This invention relates generally to nuclear waste disposal and, more particularly, is directed to the volume reduction of radioactive cruciform shaped control rods for storage.
One of the most pressing problems in the nuclear electric generation industry is the disposal of radioactive waste, and particularly of boiling water nuclear reactor (BWR) control rods. Such BWR control rods generally are formed in a cruciform shape having a length of approximately fifteen feet and an outer rectangular circumference of approximately eleven inches. The center spline of the cruciform structure is made of solid 304 stainless steel and has four equiangularly spaced flanges.
A punctured sheath of 304 stainless steel which contains a moderator is spot welded to each of the four flanges of the cruciform center. The moderator held within each sheath includes a plurality of neutron absorption rods, generally made of boron. However, the punctured sheaths have a length less than that of the control rod, and therefore do not extend to the ends of the control rod.
The control rod also includes a handle at its upper end which is made of fabricated 304 stainless steel and is welded to the body of the control rod. The control rod at the handle end is solid stainless steel and is approximately eight inches in length. A velocity limiter is provided at the opposite end of the cruciform shaped control rod, and extends approximately 24 inches along the control rod.
It is often necessary from time to time to remove worn out control rods from the nuclear reactor. This operation is performed when the control rods are extremely radioactive, that is, from 200 to 200,000 REMs/hr. Specifically, the control rods are removed and stored in a vertical position in a spent fuel pool having a depth of approximately forty feet, such that the upper ends of the spent control rods are at least five feet from the surface of the pool, thereby preventing harm from radiation exposure to operating personnel.
The principal problem with such storage is that the amount of space available in the spent fuel pool, and in transport containers, is finite. Since the control rods have a cruciform shape, however, they require a large amount of space, which is undesirable from a storage, transport and reprocessing standpoint.
In this regard, U.S. Pat. No. 4,434,092 to Mary discloses a method and apparatus of reducing the size of cruciform shaped control rods by cutting off the handle and velocity limiter ends thereof. After the ends of the control rods in Mary have been cut off, the remaining cruciform shape remains for storage. However, such cruciform shaped control rod occupies a great amount of space in the spent fuel pool.
U.S. Pat. No. 4,507,840 to Steinert et al. discloses a method of compacting nuclear reactor components in which the cruciform shaped control rod is stacked vertically, and cut sections of a hollow fuel channel are stacked in each quadrant of the cruciform shaped control rod. See also U.S. Pat. No. 4,383,394 to Qurnell et al. for the cutting of hollow fuel channels.
The Steinert et al. Patent also discusses a prior art technique for cutting the cruciform shaped control rods. Specifically, the upper and lower portions are first severed from the main body of the control rod. Then, the individual blade sections of the cruciform structure are removed from the central spine by longitudinal cuts and are then stacked and buried together. However, as recognized by Steinert et al., these latter cuts must be made quite near the central spline since the blades enclose neutron absorber rods which contain radioactive gas. Thus, the cuts are very difficult and time consuming to carry out because the nozzle of a cutting torch or the blade of a saw can not easily fit into the restricted region where the cut must be made.
U.S. Pat. No. 4,431,899 to Racki et al. discloses a laser cutting assembly for cutting a hexagonal casing which contains a plurality of tubes filled with spent nuclear reactor fuel. However, since hexagonal casings are very different from cruciform shaped control rods, this Patent is only marginally relevent to the present invention.
Other references cited in the parent application of the present application, which are less relevant than the above discussed references, but which may be relevant to the present application, are U.S. Pat. Nos. 4,021,886; 4,164,966; 4,434,092; 4,511,499; and 4,588,524; Japanese Patent Publication No. 59-116596; and British Patent Specification No. 1,437,598.